Method and apparatus for processing biologically hardly degradable waste water capable of reducing ozone

ABSTRACT

In a method for processing a biologically hardly degradable waste water including benzene ring materials, the waste water is oxidized by using ozone to produce oxalic acid. Then, the oxalic acid is reacted using a chemical reaction to produce oxalate. Finally, the oxalate is separated out from the waste water.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method and apparatus for processingbiologically hardly degradable waste water including benzene ringmaterials.

2. Description of the Related Art

Generally, organic waste water is processed by a biological process toremove organic materials from the waste water. In this case, if theorganic waste water includes biologically hardly degradable materialssuch as benzene ring materials, the hardly degradable materials arechanged into biologically easily degradable materials before thebiological process.

In a first prior art method for processing biologically hardlydegradable materials, the materials are oxidized by an oxidizer such assodium hypochlorite.

In a second prior art method for processing biologically hardlydegradable materials (see JP-A-8-192175), the materials are irradiatedwith ultraviolet rays to produce hydroxyl radical.

In a third prior art method for processing biologically hardlydegradable materials (see JP-A-9-103787), the materials with asupporting electrolyte added are electrolyzed by DC.

In a fourth prior art method for processing biologically hardlydegradable materials (see JP-A-6-126288), the materials are oxidized byusing ozone.

In the above-mentioned prior art methods, the fourth prior art method ismost effective for processing a large amount of waste water.

In the fourth prior art method, however, various kinds of oxidationprocesses may occur simultaneously due to less selectivity of ozone insuch oxidation processes, which would consume a large amount of ozone.This will be explained later in detail.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a method andapparatus for processing a biologically hardly degradable waste waterincluding benzene ring materials capable of reducing an amount ofconsumed ozone.

According to the present invention, in a method for processing abiologically hardly degradable waste water including benzene ringmaterials, the waste water is oxidized by using ozone to produce oxalicacid. Then, the oxalic acid is reacted using a chemical reaction toproduce oxalate. Finally, the oxalate is separated out from the wastewater.

Also, in an apparatus for processing a biologically hardly degradablewaste water including benzene ring materials, an oxidation cell isprovided for oxidizing the waste water using ozone to produce oxalicacid. A chemical reaction cell is connected to the oxidation cell toreact the oxalic acid using a chemical reaction to produce oxalate. Aseparation cell is connected to the chemical reaction cell to separateout the oxalate from the waste water.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be more clearly understood from thedescription set forth below, as compared with the prior art, withreference to the accompanying drawings, wherein:

FIG. 1 is a flowchart for explaining a prior art method for processingorganic waste water;

FIG. 2 is a diagram illustrating an organic waste water processingapparatus for carrying out the method as illustrated in FIG. 1;

FIG. 3 is a flowchart for explaining a first embodiment of the methodfor processing organic waste water according to the present invention;

FIG. 4 is a diagram illustrating an organic waste water processingapparatus for carrying out the method as illustrated in FIG. 3;

FIG. 5 is a flowchart for explaining a second embodiment of the methodfor processing organic waste water according to the present invention;

FIG. 6 is a diagram illustrating an organic waste water processingapparatus for carrying out the method as illustrated in FIG. 5;

FIG. 7 is a flowchart for explaining a third embodiment of the methodfor processing organic waste water according to the present invention;and

FIG. 8 is a diagram illustrating an organic waste water processingapparatus for carrying out the method as illustrated in FIG. 7.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Before the description of the preferred embodiments, a prior art methodand apparatus for processing organic waste water will be explained withreference to FIGS. 1 and 2 (see JP-A6-126288).

In FIG. 1, which is a flowchart for explaining a prior art method forprocessing organic waste water, waste water including biologicallyhardly degradable material formed by benzene ring material such as aphenolic hydroxyl group is processed.

First, at step 101, an oxidation process using ozone is performed uponthe waste water. As a result, the waste water is oxidized.

Next, at step 102, it is determined whether or not benzene ring materialstill remains in the oxidized waste water. As a result, if benzene ringmaterial remains, the control proceeds to step 101 which continues theoxidation process using ozone. On the other hand, if no benzene ringmaterial remains, the control proceeds to step 103.

At step 103, a biological process is performed upon the waste waterincluding no benzene ring material. As a result, the biological oxygendemands (BOD) value or the chemical oxygen demands (COD) value becomeslower than a predetermined value.

Next, at step 104, the waste water is ejected, thus completing theflowchart of FIG. 1 at step 105.

In FIG. 2, which illustrates a waste water processing apparatus forcarrying out the method as illustrated in FIG. 1, reference numeral 201designates an oxidation cell, and 202 designates a biological processingcell. The oxidation cell 201 is supplied with ozone via a valve 203.Also, a valve 204 is provided between the oxidation cell 201 and thebiological processing cell 202. Further, a valve 205 is connected at anoutlet of the biological processing cell 202.

The valves 203, 204 and 205 are controlled by a control circuit 206which is connected to an organic material sensor 201 a provided withinthe oxidation cell 201.

The operation of the apparatus of FIG. 2 is explained below.

When waste water is supplied to the oxidation cell 201, the controlcircuit 206 opens the valve 203, so that an oxidation process usingozone is performed upon the waste water in the oxidation cell 201. As aresult, the waste water is oxidized. In this state, the control circuit206 determines whether or not benzene ring material still remains in theoxidized waste water in accordance with the output signal of the organicmaterial sensor 201 a. When no benzene ring material remains, thecontrol circuit 206 closes the valve 203, and then, opens the valve 204.As a result, the waste water is moved from the oxidation cell 201 to thebiological processing cell 202 by a motor (not shown) or the like.

Then, a biological process is performed upon the waste water includingno benzene ring material in the biological processing cell 202. As aresult, when the BOD value or the COD value becomes lower than apredetermined value, the control circuit 206 opens the valve 205, sothat the waste water is ejected by a motor (not shown) or the like.

In the method and apparatus as illustrated in FIGS. 1 and 2, however,various kinds of oxidation processes may occur simultaneously due toless selectivity of ozone in such oxidation processes, which wouldconsume a large amount of ozone. That is, benzene ring material ischemically changed by an oxidation process into oxalic acid. Also,oxalic acid is chemically-changed by an oxidation process into formicacid. Further, formic acid is chemically-changed by an oxidation processinto carbonic acid. Note that the total ozone required for the lattertwo oxidation processes is much larger than the total ozone required forthe former oxidation process.

A first embodiment of the method for processing organic waste wateraccording to the present invention will be explained next with referenceto FIG. 3.

First, at step 301, an oxidation process using ozone is performed uponwaste water. As a result, the waste water is oxidized. In this case,although benzene rings are oxidized and opened so as to produce oxalicacid, the production speed is relatively low. Thus, the waste water mayconsist of unoxidized benzene ring material and oxalic acid.

Next, at step 302, ammonium salt(such as ammonium chloride) or ammoniaand calcium salt such as calcium hydroxide are added to the waste water.As a result, oxalic acid is chemically-changed by ammonium salt orammonia into ammonium oxalate, and then, ammonium oxalate ischemically-changed by calcium salt into calcium oxalate which isseparated out. Thus, the waste water may consist of unoxidized benzenering material and unreacted oxalic acid.

Next, at step 303, the waste water is heated to a temperature higherthan about 95° C., so that unreacted oxalic acid is chemically-changedinto oxalic amid which is separated out. Simultaneously, excess ofammonia included in the waste water is gasfied, and the excess ofammonia is fed back to the ammonium salt and calcium salt supplying step302 to reuse it.

Next, at step 304, it is determined whether or not an amount of depositformed by calcium oxalate and oxalic amid is larger than a predeterminedvalue. As a result, if the amount of deposit is larger than thepredetermined value, which means that the amount of unoxidized benzenering material is still large, the control proceeds via a depositremoving step 309 to step 301, which repeats the operation of steps 302through 304. On the other hand, if the amount of deposit is not largerthan the predetermined value, which means that the amount of unoxidizedbenzene ring material is small or negligible, the control proceeds tostep 305.

At step 305, the deposit is removed by a centrifugal separator or thelike.

At step 306, a biological process is performed upon the waste waterincluding no benzene ring material. As a result, the BOD value or theCOD value becomes lower than a predetermined value.

Next, at step 307, the waste water is ejected, thus completing theflowchart of FIG. 3 at step 308.

Note that the operation of the deposit removing step 309 is the same asthat of step 305.

In the first embodiment, since no ozone is required for processingoxalic acid, the amount of consumed ozone can be reduced.

In FIG. 4, which illustrates a waste water processing apparatus forcarrying out the method as illustrated in FIG. 3, reference numeral 401designates an oxidation cell, 402 designates a chemical reaction cell,403 designates a heating cell, 404 designates a separation cell, and 405designates a biological processing cell. Valves 406, 407, 408 and 409are provided among the cells 401 through 405, and a valve 410 isconnected at an outlet of the biological processing cell 405. Theoxidation cell 401 is supplied with ozone via a valve 411.

Also, an ammonia source 412 and a calcium hydroxide source 413 areconnected to the chemical reaction cell 402. Note that, if ammonium saltsuch as ammonium chloride is used, an ammonium salt source is providedinstead of the ammonia source 412.

Also, an ammonia feedback pipe 414 is connected between the heating cell403 and the chemical reaction cell 402 via a valve 415.

Further, a waste water feedback pipe 416 is connected between theseparation cell 404 and the oxidation cell 401 via a valve 417.

The valves 406 through 411, 415 and 417 are controlled by a controlcircuit 418 which is connected to a deposit sensor 403 a provided withinthe heating cell 403.

The operation of the apparatus of FIG. 4 is explained below.

When waste water is supplied to the oxidation cell 401, the controlcircuit 418 opens the valve 411 while closing the valve 406, so that anoxidation process using ozone is performed upon waste water in theoxidation cell 401. As a result, the waste water is oxidized. In thiscase, although benzene rings are oxidized and opened so as to produceoxalic acid, the production speed is relatively low. Thus, the wastewater in the oxidation cell 401 may consist of unoxidized benzene ringmaterial and oxalic acid.

Next, the control circuit 418 closes the valve 411, and then, opens thevalve 406 while closing the valve 407. As a result, the waste water ismoved from the oxidation cell 401 to the chemical reaction cell 402,where ammonia and calcium salt such as calcium hydroxide are added tothe waste water. As a result, oxalic acid is chemically-changed byammonia into ammonium oxalate, and then, ammonium oxalate ischemically-changed by calcium salt into calcium oxalate which isseparated out. Thus, the waste water of the chemical reaction cell 402may consist of unoxidized benzene ring material and unreacted oxalicacid.

Next, the control circuit 418 opens the valve 407 while closing thevalve 408. As a result, the waste water is moved from the chemicalreaction cell 402 to the heating cell 403, where the waste water isheated, so that unreacted oxalic acid is chemically-changed into oxalicamid which is separated out. Simultaneously, the control circuit 41opens the valve 415 so that excess of ammonia included in the wastewater is gasfied, and the excess of ammonia is fed back via the feedbackpipe 415 to the chemical reaction cell 402 to reuse it.

Next, the control circuit 418 determines whether or not an amount ofdeposit formed by calcium oxalate and oxalic amid is larger than apredetermined value. As a result, if the amount of deposit is largerthan the predetermined value, which means that the amount of unoxidizedbenzene ring material is still large, the control circuit 418 opens thevalves 408 and 417 while closing the valve 409. As a result, the wastewater is moved from the heating Cell 403 to the separation cell 404,where the deposit is removed by a centrifugal separator or the like.Then, the waste water is fed back to the oxidation cell 401 via thefeedback pipe 416.

On the other hand, if the amount of deposit is not larger than thepredetermined value, which means that the amount of unoxidized benzenering material is small, the control circuit 418 opens the valve 408while closing the valves 409 and 417. Even in this case, the waste wateris moved from the heating cell 403 to the separation cell 404, where thedeposit is removed by a centrifugal separator or the like. Then, thecontrol circuit 417 opens the valve 409 while closing the valve 410. Asa result, the waste water is moved from the separation cell 404 to thebiological processing cell 405, where a biological process is performedupon the waste water including no benzene ring material. As a result,the BOD value or the COD value becomes lower than a predetermined value.

Next, the control circuit 418 opens the valve 410, so that the wastewater is ejected.

In FIG. 5, which illustrates a second embodiment of the method forprocessing organic waste water according to the present invention, step303 of FIG. 3 is omitted. Therefore, the waste water is not heated, sothat unreacted oxalic acid is not chemically-changed into oxalic amid.Thus, no oxalic amid is produced. In addition, since excess of ammoniaincluded in the waste water is not gasfied, and the excess ammonia isnot reused.

Also, at step 304, it is determined whether or not an amount of depositformed by only calcium oxalate is larger than a predetermined value.

In FIG. 6, which illustrates a waste water processing apparatus forcarrying out the method as illustrated in FIG. 5, the heating cell 403,the valve 407, the feedback pipe 414 and the valve 415 of FIG. 4 are notprovided, and a deposit sensor 402 a instead of the deposit sensor 403 ais provided with the chemical reaction cell 402.

Even in the second embodiment, since no ozone is required for processingoxalic acid, the amount of consumed ozone can be reduced.

In FIG. 7, which illustrates a third embodiment of the method forprocessing organic waste water according to the present invention, step302 of FIG. 3 is modified into step 302′ which adds only ammonium saltor ammonia to the waste water. As a result, at step 302′, althoughoxalic acid is chemically-changed by ammonium salt or ammonia intoammonium oxalate, ammonium oxalate is not chemically-changed by calciumsalt into calcium oxalate. Therefore, calcium oxalate is not separatedout.

Also, at step 303, the waste water is heated, so that unreacted oxalicacid is chemically-changed into oxalic amid which is separated out.Simultaneously, excess of ammonia included in the waste water isgasfied, and the excess of ammonia is fed back to the ammonium salt andcalcium salt supplying step 302 to reuse it.

Further, at step 304, it is determined whether or not an amount ofdeposit formed by only oxalic amid is larger than a predetermined value.

In FIG. 8, which illustrates a waste water processing apparatus forcarrying out the method as illustrated in FIG. 7, the elements are thesame as those of FIG. 4 except that the calcium hydroxide source 413 ofFIG. 4 is not provided.

Even in the third embodiment, since no ozone is required for processingoxalic acid, the amount of consumed ozone can be reduced.

As explained hereinabove, according to the present invention, the amountof consumed ozone can be reduced.

What is claimed is:
 1. A method for processing a biologically hardlydegradable waste water including benzene ring materials, comprising thesteps of: oxidizing said waste water using ozone to produce oxalic acid;reacting said oxalic Acid using a chemical reaction to produce oxalate;and separating out said oxalate from said waste water.
 2. The method asset forth in claim 1, wherein said oxalic acid reacting step comprises astep of adding one of ammonium salt and ammonia as well as calcium saltto said waste water, so that said oxalate is made of calcium oxalate. 3.The method as set forth in claim 1, further comprising a step of heatingsaid waste water to a temperature higher than about 95° C. so thatunreacted waste water is chemically-changed into oxalic amid, saidoxalate being made of said oxalic amid as well as said calcium oxalate.4. The method as set forth in claim 3, further comprising a step offeeding back ammonia produced in said heating step to said waste wateras said one of ammonium salt and ammonia.
 5. The method as set forth inclaim 1, further comprising the steps of: determining whether or not anamount of said oxalate is smaller than a predetermined value; andrepeating operations of said oxidizing and chemical reacting steps, onlywhen the amount of said oxalate is smaller than said predeterminedvalue.
 6. The method as set forth in claim 1, wherein said oxalic acidreacting step comprises a step of adding one of ammonium salt andammonia to said waste water; said method further comprising a step ofheating said waste water to a temperature higher than about 95° C. sothat said oxalate is made of said oxalic amid.
 7. The method as setforth in claim 6, further comprising a step of feeding back ammoniaproduced in said heating step to said waste water as said one ofammonium salt